Filler and wax composition for investment casting

Abstract

Thermoplastic resin powders of cellulose acetate esters in which essentially 80% or more of the particles pass through a 100 mesh screen (U.S. Sieve Series) and essentially 50% pass through a 200 mesh screen (U.S. Sieve Series) are desirable and useful as a filler material for investment casting waxes. The cellulosic thermoplastics resin powders are environmentally safe when used as filler material for investment casting wax compositions since the powders produce essentially no carcinogenic materials on combustion. The powders are as effective as acid fillers and set relatively fast thus improving cycle time in the die but do not produce an adverse effect of shell cracking nor react with the slurry.

I claim: 
     
       1. In an investment casting wax composition for use in an investment casting wax process, the improvement wherein particles of a cellulose acetate resin are present in the composition as a filler. 
     
     
       2. An investment casting wax composition according to claim 1 wherein at least about 80% by weight of the cellulose acetate resin particles pass through a 100 mesh screen and at least about 50% by weight of the particles pass through a 200 mesh screen. 
     
     
       3. An investment casting wax composition according to claim 2 wherein the cellulose acetate resin is cellulose acetate having a specific gravity of about 1.31 to 1.32. 
     
     
       4. An investment casting wax composition according to claim 3 wherein the cellulose acetate resin particles comprise from about 15 to about 25% by weight of the investment casting wax composition. 
     
     
       5. An investment casting wax composition according to claim 3 wherein the cellulose acetate resin particles comprise from about 5 to about 100% by weight of the total filler in the investment casting wax composition. 
     
     
       6. An investment casting wax composition according to claim 2 wherein the cellulose acetate resin powder particles comprise from about 5 to about 75% by weight of the investment casting wax composition. 
     
     
       7. An investment casting wax composition according to claim 2 wherein the cellulose acetate resin particles comprise from about 15 to about 25% by weight of the investment casting wax composition. 
     
     
       8. An investment casting wax composition according to claim 5 wherein the cellulose acetate resin particles comprise from about 5 to about 100% by weight of the total filler in the investment casting wax composition. 
     
     
       9. An investment casting wax composition according to claim 2 wherein the cellulose acetate resin particles comprise from about 5 to about 100% by weight of the total filler in the investment casting wax composition. 
     
     
       10. An investment casting wax composition according to claim 1 wherein the cellulose acetate resin particles comprise from about 5 to about 100% by weight of the total filler in the investment casting wax composition. 
     
     
       11. An investment casting wax composition for use in the investment casting wax process which consists essentially of a base wax composition melting in the range of 120° to 200° F. and, as a filler, about 10 to 55% by weight of the final composition of cellulose acetate resin powder particles wherein at least about 80% by weight of said particles pass through a 100 mesh screen and at least about 50% by weight passes through a 200 mesh screen, said wax composition having sufficient hardness to form acceptable patterns and said wax composition being dimensionally stable. 
     
     
       12. A composition of claim 11 wherein the base wax comprises about 0 to 15 wt. % vegetable wax, about 20 to 60 wt. % petroleum wax consisting of a mixture of paraffins having a melting point of from 120° to 160° F. and microcrystalline waxes having a melting point of from about 135° to 205° F., about 1 to 12 wt. % synthetic waxes and about 13 to 79 wt. % of resins selected from hydrocarbon resins and resins derived from the refining of petroleum or of wood products. 
     
     
       13. A composition of claim 12 wherein the vegetable wax is carnauba wax. 
     
     
       14. A composition of claim 12 wherein the vegetable wax is candelilla wax. 
     
     
       15. A low shrinkage, dimensionally stable investment casting wax composition having sufficient hardness to form acceptable patterns for use in the investment casting wax process which consists essentially of a base wax melting in the range of 120° to 200° F. and, as a filler, from about 5 to about 75% by weight of particles of a cellulose acetate resin powder particles wherein at least about 80% by weight of said particles pass through a 100 mesh screen and at least about 50% by weight passes through a 200 mesh screen. 
     
     
       16. An investment casting wax composition of claim 15 of the following composition: 37.50 weight percent of polyterpene resin having a specific gravity of 0.995 (25°/25° C.) and a ball and ring softening point of about 135° C.; 20.25 weight percent of paraffin wax having a softening point at about 155° F.; 13.50 weight percent of microcrystalline wax having a softening point at about 178° F.; 3.75 weight percent of polyethylene softening in the range of 244° to 262° F. and 25.00 weight percent of said cellulose acetate particle filler. 
     
     
       17. An investment casting wax composition of claim 15 of the following composition: 40 weight percent of polyterpene resin having a specific gravity of 0.995 (25°/25° C.) and a ball and ring softening point of about 135° C.; 21.6 weight percent of paraffin wax having a softening point at about 155° F.; 14.4 weight percent of microcrystalline wax having a softening point at about 178° F.; 4.0 weight percent of polyethylene softening in the range of 244° to 262° F. and 20.0 weight percent of said cellulose acetate particle filler. 
     
     
       18. An investment casting wax composition of claim 15 of the following composition: 30.95 weight percent of a hydrogenated C 5 , C 9  resin; 22.75 weight percent of paraffin wax having a softening point of about 145 ° F.; 22.75 weight percent of microcrystalline wax having a softening point of about 178° F.; 9.10 weight percent of candelilla wax; 4.55 weight percent montan wax; 0.91 weight percent synthetic paraffin wax; and 9.0 weight percent of said particle filler. 
     
     
       19. An investment casting wax composition of claim 15 of the following composition: 8.4 weight percent carnauba wax, 15.1 weight percent microcrystalline wax having a softening point of about 178° F.; 14.3 weight percent paraffin wax having a softening point of about 145° F.; 4.2 weight percent of polyethylene having a softening point of about 222° F.; 42.0 weight percent of an aliphatic hydrocarbon resin having a softening point of about 115° C.; and 16.0 weight percent of said cellulose acetate particle filler. 
     
     
       20. A method for investment casting comprising: (a) forming in a mold a thermoplastic pattern of an investment casting wax composition, said investment casting composition comprising a base wax composition and from about 5 to about 75% by weight, based on the weight of the base wax composition, of particles of a cellulose acetate resin powder particles as a filler; and   (b) investing said pattern to form a east.